This invention relates to a web surface treating apparatus and particularly to apparatus for calendaring the surface of webs such as magnetic tape webs used for manufacture of magnetic storage disks, carbonless coated paper webs and the like.
In the manufacture of relatively thin film products, the base material may be advantageously provided in large rolls of appropriate web material. The product is then made from the web material through suitable automated machinery. In various applications the surface of the web material should be finely finished to provide the proper end product. A typical example is finishing of a magnetic film which is subsequently used as a source for manufacture of magnetic floppy disks and the like. Carbonless coated paper web is another example where calendaring is desirable to form a compact skin which is firmly affixed to the base. Various devices to calendar the surface have been manufactured and are commercially available. Although a horizontally arranged unit is available, the units generally have been made of a series of vertically stacked rolls including two intermediate fabric covered rolls located between three alternating steel rolls. The steel rolls are normally chrome or stainless surfaced and provided with highly finished mirror finish. The web is fed from a suitable sources and threaded through the rolls. In appropriate polishing and finishing of the web, the pressure applied to the web and the temperature of the web are relatively critical factors which must be appropriately controlled and maintained. The steel rolls include controllable heat means for controlling the temperature of the rolls and thereby the temperature of the web. As the web passes through the nip of the rolls, the working of the material may result in significant changes in the temperature. This requires appropriate changes in the temperature of the rolls.
Generally, the prior art has used various forms of heating including electrical heating cartridges and flow of a heated liquid through passageways in the steel roll and the like to control the temperature of the web. In addition, the rolls are appropriately positioned through pneumatic or hydraulic loading to control the nip pressure.
Although the various systems have been suggested and are available, the control of the pressure and temperature continues as a problem with respect to optimum results and life. In vertically oriented systems, it is quite difficult to control the pressure systems. In the prior art heating controls, the response time has been quite long, on the order of 5 to 10 minutes. Because of the long response period, it is extremely difficult to maintain the web at the proper temperature.
Thus, there remains a need for a calendaring apparatus and other roll type apparatus having means for accurate and rapid change in the temperature of the roll as well as appropriate, convenient processing of the web with control of the nip pressure.